Method for heat treating metallic strip material

ABSTRACT

A method for heat treating metallic strip stock in cylindrical form by drawing the strip stock through a funnel-shaped element and then through a heated tube, characterized in that a protective sheet is passed through the heated tube along with the metallic strip stock to be heat treated such that it encircles and envelops the cylindrical form to be heat treated and prevents damage to its outer surface due to frictional drag between the heated tube and the cylindrical form passing therethrough.

United States Patent Hayden, Jr. et al.

[15] 3,655,460 Apr. 11, 1972 [54] METHOD FOR HEAT TREATING METALLIC STRIP MATERIAL John T. Hayden, Jr., Richmond, Va.; Casimir F. Plasewiez, Baltimore, Md.

Inventors:

Assignee: Westinghouse Electric Corporation, Pittsburgh, Pa.

Filed: June 24, 1970 Appl. No.: 49,430

U.S. Cl ..l48/13.1, 148/13.2, 148/14, 148/127, 148/156, 148/160 Int. Cl. ..C21d 1/34 Field ofSearch ..148/13,13.1,13.2,l4,127, 148/156, 160

[56] References Cited UNITED STATES PATENTS 2,989,428 6/1961 Wilson... 3,421,950 1/1969 Frehn ..148/l3.l

Primary Examiner-Richard 0. Dean Attorney-F. H. Henson and E. P. Klipfel [5 7] ABSTRACT A method for heat treating metallic strip stock in cylindrical form by drawing the strip stock through a funnelshaped element and then through a heated tube, characterized in that a protective sheet is passed through the heated tube along with the metallic strip stock to be heat treated such that it encircles and envelops the cylindrical form to be heat treated and prevents damage to its outer surface due to frictional drag between the heated tube and the cylindrical form passing therethrough.

7 Claims, 4 Drawing Figures METHOD FOR HEAT TREATING METALLIC STRIP MATERIAL CROSS-REFERENCES TO RELATED APPLICATIONS BACKGROUND OF THE INVENTION While not limited thereto, the present invention is particularly adapted for use in the production of booms used for stabilization purposes on orbiting satellites. These booms, carried on the satellite in the form of coiled strips of metal, can be paid off a reel on which they are carried after the satellite is in orbit in much the same manner as a tape measure. As the strip issues from the reel on which it is formed, it curls into a tubular form having an axis extending along the movement of the strip as it issues from its storage reel. These tubular forms, usually four in number, may extend out from the satellite in excess of 100 feet, forming an X with the satellite at the intersection. Small differences in gravitational attraction for each of the tip masses of the booms, due to some of the masses being further from the earth than the others, act to orient the satellite until the gravitational attraction on the respective booms is equalized.

As mentioned above, the booms are stored as metal strips on reels inside the spacecraft. When they are to be deployed, the reels are unwound and the spring tension built into the metal strips by a precipitation hardening treatment curls them into tubes about a half inch in diameter. The edges of the strips are notched so that they interlock and keep the formed booms stiff.

Such booms may be formed from an alloy of copper, beryllium and cobalt, such as about 2 percent beryllium, 0.25 percent cobalt and the remainder copper. The outer surface of the strip which forms the boom must be coated with a layer of metal, such as aluminum, which is reflecting; while the inner surface of the boom is coated with a layer of cupric oxide, which is black. By providing openings in the boom along its length, the radiation absorbed by the black interior and that reflected from the exterior equalize the temperatures at the inner and outer surfaces of the tubular boom so as to prevent thermally induced bending stresses.

Alloys of beryllium and copper of this type, when precipitation hardened at a suitable temperature, have a memory meaning that when they are heat treated as a thin sheet, they will tend to snap back into the shape they were in during heat treating. Advantage is taken of this in forming stabilizing booms for satellites. The beryllium-copper alloy in sheet form is drawn through a funnel-shaped element such that it curls into a tubular configuration and thereafter is drawn through a heated tube where it is heat treated. The emerging strip assumes a permanent set" as a split tube; however, because of its thinness and relative flexibility, it can be wound back into a reel as flat stock. When unreeled on the satellite, it again assumes it tubular configuration.

As one example of a method for heat treating sheet stock such that it will assume a tubular configuration when unreeled, perforated beryllium-cobalt-copper flat tape having a gauge of about 0.002 inch and a width of about 1.725 inches is fed into a glass or metal furnace tube having a diameter of about one-half inch and a length of about 4 feet, with the entrance end shaped in the form of a funnel. The tape is drawn through the tube at a constant drawing rate equivalent to about 8 minutes at 700 F.

Although the forming operation is dependent upon friction as well as temperature to close the flat tape into its final tubular form, excessive friction and drag are detrimental to the finished boom. As was mentioned above, the tape is coated on its outer surface with a reflective metal such as aluminum; and as a result of the friction and drag at the aluminum-glass or aluminum-metal furnace tube interface, a build-up of metallic aluminum and aluminum oxide occurs on the inner walls of the furnace tube. This build-up increases as successive lengths of boom are formed, thus increasing friction and drag. As a consequence, the aluminum coating is severely scratched and the beryllium-cobaIt-copper base metal is penetrated to a depth sufficient to cause structural weakness in the formed boom.

To alleviate this problem, various lubricants, forming tubes, and entrance funnels have been used without success. In some instances, lubricants reduced the damage to the aluminum coating but destroyed the black cupric oxide inner coating. In other instances, the lubricants used could not be removed effectively from the finished booms.

SUMMARY OF THE INVENTION In accordance with the present invention, damage to the outer surface of a metallic strip in tubular form passing through a heated tube is prevented by feeding into the tube, along with the metallic strip material to be heat treated, a second strip of protective material which encircles and encapsulates the tubular form as it passes through the heat-treating tube. In this manner, the second strip, rather than the surface of the workpiece, is in frictional contact with the inner surface of the tube so as to prevent damage to the surface of the workpiece being heat treated. The protective strip is preferably a plastic material which will withstand the necessary heat treating time and temperature and which will not itself build up a deposit on the inside of the tube. Alternatively, the protective strip may comprise a strip of aluminum or stainless steel foil, for example.

The protective strip is preferably stored on a reel, paid off into the heating tube along with the material to be heat treated, and thereafter rewound on a second reel at the other end of the tube while the heat-treated material is also rewound on a separate reel.

The above and other objects and features of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings which form a part of this specification, and in which:

FIG. 1 is a top or plan view of the metallic strip material in flat form which is to be heat treated in accordance with the process of the invention;

FIG. 2 is a perspective view of a tubular structure formed from the flat strip stock of FIG. I; and

FIGS. 3A and 3B illustrate the manner in which flat strip stock is formed into the tubular configuration of FIG. 2 in a precipitation hardening treatment.

With reference now to the drawings, and particularly to FIG. 1, flat, perforated strip stock 10 is shown which, in one embodiment of the invention, is formed from a berylliumcobalt-copper alloy, typically containing about 2 percent beryllium, 0.25 percent cobalt and the remainder copper. An alloy of this type, as mentioned above, has a memory meaning that when it is heat treated for a suitable time and at a suitable temperature in a certain configuration, it will tend to snap back into that configuration after it is heat treated. As shown in FIG. 1, the strip 10 is provided with perforations or openings 12 throughout its surface as well as notches 14 along one edge. The notches 14 are adapted to cooperate with notches 16 on the other side of the strip material when the flat strip stock shown in FIG. 1 is formed into a tubular configuration with the notches 14, for example, snapping into the notches 16. The strip 10 has formed on one side thereof a layer of cupric oxide which is black and on the other side thereof is coated with a reflective material, such as aluminum.

A full and complete description of the manner in which the strip stock shown in FIG. 1 is formed can be had by reference to copending application Ser. No. 742,191, filed July 3, 1968 and assigned to the Assignee of the present application. Briefly, it is formed with a starting material comprising a copper-base alloy strip supplied in the solution treated, unaged but half-hard temper condition, preferably with a highly polished surface. This material is then subjected to vapor phase degreasing following which one surface of the strip material is provided with a black copper oxide coating, without the benefit of any sort of intermediate metallic plating. This is provided by applying a lacquer to the side of the strip opposite that which is to be coated with the black cupric oxide, by then pickling the unlacquered side of the strip material, and finally by passing the strip through a blackening solution such as a solution of sodium hydroxide and sodium chlorate to form a layer of cupric oxide which is black.

Following the application of the black cupric oxide to the one surface of the strip, the lacquer mask is dissolved by the use of an organic solvent to prepare the strip for the next step which is milling by an etching process to provide the plurality of perforations or openings 12. Following such milling, the surface of the strip opposite that containing the cupric oxide is subjected to an aluminum vapor-deposition process, thereby forming the reflective surface on one side of the strip.

The starting material for forming tubular booms in accordance with the invention is initially flat and, in the absence of any heat treatment will remain flat as shown in FIG. 1. However, if it is bent into a tubular configuration as shown in FIG. 2 and heated at a specified temperature for a predetermined perioed of time, precipitation hardening occurs such that it will assume a permanent set, even when cooled after the heat treating process, wherein it tends to curl into the tubular configuration of FIG. 2. In this manner, precipitation hardened strip stock of FIG. 1, now in the form of a tube such as that shown in FIG. 2, can be flattened and rewound upon a reel such that then it is paid off the reel, it will again assume the tubular configuration of FIG. 2 and may be used, for example, to form a boom for a satellite. Note in FIG. 2 that the notches 16 interlock with the notches 14 to provide an overlapped portion. The outer surface of the tubular configuration shown in FIG. 2 is reflective; while the inner surface is coated with cupric oxide and is black as described above.

The manner in which the sheet of FIG. 1 is heat treated to form the configuration of FIG. 2 is shown in FIGS. 3A and 3B. The strip stock is stored on a reel 18 and is drawn through a tube 20 having a funnel-shaped element 22 at the forward end thereof. Before it passes through tube 20, it is flat or planar and tends to remain flat. The bottom surface 24 of the strip stock 10 is coated with aluminum or some other reflective material; while the upper surface 26 is coated with cupric oxide. The other end of the strip stock 10 is connected to a reel 28 which is driven by any suitable drive means, not shown, to thereby draw the strip stock through the tube 20. The flat strip stock 10 may typically have a gauge of about 0.002 inch and a width of about 1.725 inches. The inner diameter of the tube 20 may typically be about one-half inch in diameter and 4 feet in length. It is heated within a furnace, not shown, to a temperature of about 700 F.

The strip material, as it is drawn into the funnel-shaped element 22, will assume a cylindrical configuration with the notches 14 and 16 interlocking as shown in FIG. 2. As it travels through the tube 20, it is heat treated and thereby assumes a permanent set in a tubular or cylindrical configuration, as it issues from the tube 20, is rewound upon the reel 28 in flat strip form. However, if the flat strip on reel 28 is unwound, it will again assume the cylindrical configuration shown in FIG. 2 with the notches l4 and 16 interlocking. It is in this manner that tubular booms are extended outwardly from a satellite. That is, the flat strip stock on reel 28, for example, is unwound; and as it does, it automatically assumes the cylindrical configuration of FIG. 2.

As was mentioned above, if strip material of the type shown in FIG. 1 is heated in a tube without any protective coating, the outer aluminum-coated surface of the strip will slide along the inner surface of the tube. This, however, results in excessive drag and friction between the inner periphery of the tube 20 and the strip 24. To alleviate the problem, various lubricants have been applied to the strip 24, but without success. In some instances, the lubricants reduced the damage to the aluminum coating but destroyed the black cupric oxide inner coating. In other instances, the lubricants used could not be efiectively removed from the finished booms.

In accordance with the present invention, a second strip 30 of protective material wound upon a reel 32 is fed into the funnel-shaped element and through the tube 20 along with the strip 24 such that the protective strip 30 encircles and envelops the tubular form as it travels through the tube 20. At the exit end of the tube 20, the protective sheet 30 is rewound upon a second reel 34. The strip 30 may be formed from metal, plastic or similar material and may comprise any material that will withstand the forming temperature of 700 F. At the same time, it must be free of by-products detrimental to either the aluminum coating, the beryllium-cobalt-copper alloy, or the inner coating of black cupric oxide. Preferably, the strip 30 comprises a polyirnide sold under the trademark KAPTON by DuPont Company, Wilmington, Delaware. Alternatively, however, it may comprise an aluminum, stainless steel or the like foil.

The present invention thus provides a means for heat treating strip stock as it passes through a tube while preventing damage to the outer surface of the strip stock as it passes through the tube. Although the invention has been shown in connection with a certain specific embodiment, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

We claim as our invention:

1. In the method for heat treating strip stock by causing the stock to pass through a funnel-shaped element and through a heated tube with the strip stock being in cylindrical form as it passes through the heated tube; the improvement which comprises passing through the heated tube simultaneously with the strip stock to be heat treated a second strip of material which encircles and envelops the strip stock to protect the surface of the strip stock from damage as it passes through the heated tube.

2. The method of claim 1 wherein said strip stock and said second strip of material are paid off from reels and passed through said funnel-shaped element into said heated tube simultaneously, and including the step of rewinding the strip stock and said protective strip on separate reels at the exit end of said heated tube.

3. The method of claim I wherein said strip stock comprises an alloy of beryllium, cobalt and copper.

4. The method of claim 1 including the step of heating said tube and the strip stock passing therethrough to a temperature of about 700F.

5. The method of claim 1 wherein said strip stock comprises a copper-base alloy which, when it is in said cylindrical form, has an outer surface coated with a reflective metal and an inner surface which is black.

6. The method of claim 5 wherein said outer surface is coated with aluminum and said inner surface comprises cupric oxide.

7. The method of claim 5 wherein, said strip is apertured. 

2. The method of claim 1 wherein said strip stock and said second strip of material are paid off from reels and passed through said funnel-shaped element into said heated tube simultaneously, and including the step of rewindiNg the strip stock and said protective strip on separate reels at the exit end of said heated tube.
 3. The method of claim 1 wherein said strip stock comprises an alloy of beryllium, cobalt and copper.
 4. The method of claim 1 including the step of heating said tube and the strip stock passing therethrough to a temperature of about 700* F.
 5. The method of claim 1 wherein said strip stock comprises a copper-base alloy which, when it is in said cylindrical form, has an outer surface coated with a reflective metal and an inner surface which is black.
 6. The method of claim 5 wherein said outer surface is coated with aluminum and said inner surface comprises cupric oxide.
 7. The method of claim 5 wherein said strip is apertured. 